The present invention relates to a rolling bearing used for various machineries in the industrial fields of automobiles, electricity, information processing, steel and others, and various types of metal cutting-machine tools and industrial machinery.
FIG. 1 typically illustrates a deep-raceway rolling bearing, which is used for various machineries in the industrial fields of automobiles, electricity, information processing, steel and others, and various types of metal cutting machine tools and industrial machinery. Design requirements of the rolling bearing 1 are: its lifetime is long, and its torque, e.g., starting torque and dynamic friction torque, are low.
The deep-raceway rolling bearing 1 illustrated in FIG. 1 is an assembly made up of inner and outer rings or races 2 and 3, circular in section but annular as a whole, and a plural number of rolling elements 4, e.g., balls, which are located and rotated between the inner and outer rings 2 and 3.
A rotary shaft 5 indicated by a long and two short dashed line is fastened to the inner periphery surface of the inner ring 2. The inner ring 2 and the rotary shaft 5 are rotatable in unison about the axial line P of the rotary shaft 5 with respect to the outer ring 3.
A raceway 8, circular in cross section, is formed in and along a contact surface of the inner ring 2 where the inner ring comes in contact with the balls. Similarly, a raceway 9, circular in cross section, is formed in and along a contact surface of the outer ring 3 where the outer ring comes in contact with the balls. In the general design of the inner raceway 8 of the inner ring 2 of the deep-raceway ball bearing 1, the radius of curvature of the raceway 8 is selected to have a value of 52% of the diameter da of the deep-raceway ball bearing 1.
The structure of the conventional deep-raceway ball bearing 1 has the following inherent features:
1) a distance between the axial line P of the rotary shaft 5 and the inner-raceway diameter 36 as the bottom of the inner raceway 8 of the inner ring 2 is not equal to a distance between the axial line P of the rotary shaft 5 and the outer-raceway diameter 37 as the bottom of the outer raceway 9 of the outer ring 3; and PA1 2) the curvature direction of the inner raceway 8 with respect to each ball 4 is not coincident with that of the outer raceway 9 with respect to the same.
Because of those features, a maximum surface contact pressure between the inner raceway 8 of the inner ring 2 and each of the balls 4 is larger than that between the outer raceway 9 of the outer ring 3 and each ball 4. A so-called flaking phenomenon, in which the contact surface of the inner raceway 8 of the outer peripheral surface 6 of the inner ring 2 separates or falls in flakes, is liable to occur on the contact surface. This phenomenon reduces the lifetime of the deep-raceway ball bearing 1.
Because of the distance difference and the curvature difference that are already mentioned, a contact area between the outer raceway 9 of the outer ring 3 and the rolling element 4 is larger than that between the inner raceway 8 of the inner ring 2 and the rolling element 4. Thence, a contact pressure between the inner ring 2 and the balls 4 is larger than that between the outer ring 3 and the balls 4, so that the inner ring 2 flakes earlier than the outer ring 3. The result is to reduce the lifetime of the deep-raceway ball bearing 1.
A contact ellipse (that is, area of the contact surface) between the outer ring 3 and the ball 4 is larger than that between the inner ring 2 and the ball 4, so that the outer ring 3 is subject to a torque larger than the inner ring 2, and the outer ring 3 has a large contribution to heat generation as compared with the inner ring 2. This increases the torque and to promotes heat generation in the whole ball bearing.